Stimulation of MAP kinase and S6 kinase by vanadium and selenium in rat adipocytes

An epigenome-wide study of selenium status and DNA methylation in the Strong Heart Study

BACKGROUND

Selenium (Se) is an essential nutrient linked to adverse health endpoints at low and high levels. The mechanisms behind these relationships remain unclear and there is a need to further understand the epigenetic impacts of Se and their relationship to disease. We investigated the association between urinary Se levels and DNA methylation (DNAm) in the Strong Heart Study (SHS), a prospective study of cardiovascular disease (CVD) among American Indians adults.

METHODS

Selenium concentrations were measured in urine (collected in 1989-1991) using inductively coupled plasma mass spectrometry among 1,357 participants free of CVD and diabetes. DNAm in whole blood was measured cross-sectionally using the Illumina MethylationEPIC BeadChip (850 K) Array. We used epigenome-wide robust linear regressions and elastic net to identify differentially methylated cytosine-guanine dinucleotide (CpG) sites associated with urinary Se levels.

RESULTS

The mean (standard deviation) urinary Se concentration was 51.8 (25.1) μg/g creatinine. Across 788,368 CpG sites, five differentially methylated positions (DMP) (hypermethylated: cg00163554, cg18212762, cg11270656, and hypomethylated: cg25194720, cg00886293) were significantly associated with Se in linear regressions after accounting for multiple comparisons (false discovery rate p-value: 0.10). The top hypermethylated DMP (cg00163554) was annotated to the Disco Interacting Protein 2 Homolog C (DIP2C) gene, which relates to transcription factor binding. Elastic net models selected 425 hypo- and hyper-methylated DMPs associated with urinary Se, including three sites (cg00163554 [DIP2C], cg18212762 [MAP4K2], cg11270656 [GPIHBP1]) identified in linear regressions.

CONCLUSIONS

Urinary Se was associated with minimal changes in DNAm in adults from American Indian communities across the Southwest and the Great Plains in the United States, suggesting that other mechanisms may be driving health impacts. Future analyses should explore other mechanistic biomarkers in human populations, determine these relationships prospectively, and investigate the potential role of differentially methylated sites with disease endpoints.

Insulin Receptor Substrates Regulation and Clinical Responses Following Vanadium-Enriched Yeast Supplementation in Obese Type 2 Diabetic Patients: a Randomized, Double-Blind, Placebo-Controlled Clinical Trial

Increasing evidence suggests that organic vanadium compounds are bioavailable and safe therapeutic agents with insulin-mimetic and insulin-enhancing features. The objective of the current study was to examine the effect of vanadium-enriched yeast (VEY) supplementation on the gene expression level of insulin receptor substrates and clinical manifestations of obese type 2 diabetic mellitus (T2DM) patients. In this randomized, double-blind, placebo-controlled clinical trial, 44 obese T2DM patients were randomly allocated into either VEY (0.9 mg/day vanadium pentoxide) or placebo group for 12 weeks. The mRNA expression level of protein tyrosine phosphatase 1B (PTP1B), phosphatase and tensin homolog (PTEN), mitogen-activated protein kinase (MAPK), ribosomal protein S6 kinase (S6K), and nuclear factor kappa-light-chain-enhancer of activated B cells (NFƘB) genes in the peripheral blood mononuclear cells, serum levels of metabolic parameters, anthropometric indices, as well as the quality of life, and dietary intake were collected at pre- and post-intervention phases. Analysis of covariance was performed to obtain the corresponding effect size. Results showed that VEY administration significantly decreased anthropometric indices and glycemic parameters and increased insulin sensitivity after adjusting for potential covariates (p < 0.05), in comparison to the placebo group. Additionally, VEY supplementation was significantly effective on MAPK, PTP1B, and NFƘB gene expression level, compared to the placebo group. No significant changes were noticed for dietary intake, quality of life, and lipid profile in the VEY group, compared to the placebo group. Overall, VEY supplementation can be considered as a promising safe adjunct therapy for improving anthropometric indices and glycemic parameters in T2DM patients.

Ameliorative effect of selenium yeast in combination with pioglitazone on diabetes outcomes in streptozotocin-induced

Anti-diabetic therapies possess many side effects; thus, searching for alternative strategies with low cost, minimal side effects, and high therapeutic value is very important. The present study aimed to explore the combined use of selenium yeast (SY) and standard anti-diabetic drug pioglitazone (PGZ) for diabetes mellitus (DM) treatment in streptozotocin (STZ)-induced DM. STZ was injected daily intraperitoneally with a low dose (40 mg/kg) into Sprague-Dawley rats to induce DM. The synergistic effect of the SY (0.2 mg/kg) and PGZ (0.65 mg/kg) on DM complications was evaluated after 88 weeks of treatment. The impact of our medication on glucose levels, insulin sensitivity, lipid abnormalities, oxidative mediators, and inflammatory markers was assessed by biochemical techniques. STZ-induced diabetes has toxic effects, including toxic hepatic tissues, lipid disturbances, massive oxidative damage, and hyperinflammation. Experimental rats either treated with monotherapy alone or combined therapy resulted in a significant anti-diabetic effect. The PGZ+ SY combination has the best effect, as illustrated by significant (P < 0.05) decreases in fasting blood glucose, (FBG) insulin, HbA1c, and HOMA-IR levels. This combination attenuated (P < 0.05) lipid disturbances and their associated elevated atherogenicity biomarkers. At the same time, treatments with PGZ+ SY exhibited an anti-inflammatory effect as they ameliorated the increase in inflammatory parameters (CRP, TNF-α, IL-6). Also, it restored the total antioxidant capacity and peroxisome proliferator-activated receptor (PPARƔ) levels that were decreased by STZ-DM induction. In conclusion, this study finds PGZ+ SY as a promising DM therapeutic alternative. This synergistic combination alleviates most DM-related complications and insulin resistance.

Emerging roles of selenium on metabolism and type 2 diabetes

Selenium is recognized as an essential element for human health and enters human body mainly via diet. Selenium is a key constituent in selenoproteins, which exert essential biological functions, including antioxidant and anti-inflammatory effects. Several selenoproteins including glutathione peroxidases, selenoprotein P and selenoprotein S are known to play roles in the regulation of type 2 diabetes. Although there is a close association between certain selenoproteins with glucose metabolism or insulin resistance, the relationship between selenium and type 2 diabetes is complex and remains uncertain. Here we review recent advances in the field with an emphasis on roles of selenium on metabolism and type 2 diabetes. Understanding the association between selenium and type 2 diabetes is important for developing clinical practice guidelines, establishing and implementing effective public health policies, and ultimately combating relative health issues.

Synergistic effect of micronutrients and metformin in alleviating diabetic nephropathy and cardiovascular Dysfunctioning in diabetic rat

Purpose

Diabetic nephropathy (DN) and Cardiovascular Dysfunctioning (CVD) are interlinked with each other and one of the leading causes of irreversible renal damage and cardiovascular disease. Micronutrients play an effective role in type-2 diabetes (T2D) and its related complications. Our work aimed to elucidate the effect of micronutrients alone and in combination with standard anti-diabetic drug metformin on DN and CVD using streptozotocin induced diabetes in rats.

Methods

T2D was induced with a single intraperitoneal (i.p.) injection of freshly prepared streptozotocin (55 mg/kg), 15 min after intraperitoneal injection of nicotinamide (230 mg/kg). Commercially available kits were used to measure kidney parameters and cardiac marker level. Creatinine clearance was calculated by using formula and heart rate was recorded using powerlab software.

Results

Significant decrease in blood glucose levels were observed 14 days after initial administration in metformin treated, micronutrients treated and metformin with micronutrients treated groups compared with diabetic group. After 6 weeks of metformin and micronutrients treatment, serum creatinine, blood urea nitrogen (BUN) and lactate dehydrogenase (LDH) levels were significantly decreased as compared to diabetic group. Moreover, urine creatinine level, creatinine clearance and heart rate (HR) was increased significantly in metformin and micronutrients treated group compared with a diabetic group. Micronutrients therapy also normalised the general symptoms of diabetes.

Conclusion

The results obtained from this study indicate the synergistic effect of metformin and micronutrients against diabetic heart and kidney. Therefore, micronutrients may be used as an effective add-on therapy for DN and CVD.

Selenium and Selenoproteins in Adipose Tissue Physiology and Obesity

Selenium (Se) homeostasis is tightly related to carbohydrate and lipid metabolism, but its possible roles in obesity development and in adipocyte metabolism are unclear. The objective of the present study is to review the current data on Se status in obesity and to discuss the interference between Se and selenoprotein metabolism in adipocyte physiology and obesity pathogenesis. The overview and meta-analysis of the studies on blood Se and selenoprotein P (SELENOP) levels, as well as glutathione peroxidase (GPX) activity in obese subjects, have yielded heterogenous and even conflicting results. Laboratory studies demonstrate that Se may modulate preadipocyte proliferation and adipogenic differentiation, and also interfere with insulin signaling, and regulate lipolysis. Knockout models have demonstrated that the selenoprotein machinery, including endoplasmic reticulum-resident selenoproteins together with GPXs and thioredoxin reductases (TXNRDs), are tightly related to adipocyte development and functioning. In conclusion, Se and selenoproteins appear to play an essential role in adipose tissue physiology, although human data are inconsistent. Taken together, these findings do not support the utility of Se supplementation to prevent or alleviate obesity in humans. Further human and laboratory studies are required to elucidate associations between Se metabolism and obesity.

Benefits of the consumption of Brazil nut (Bertholletia excelsa) extract in male reproductive parameters of streptozotocin-induced diabetic rats

Objective

The objective of this study was to evaluate the effects of intake of Brazil nut extract (BN) or sodium selenite solution on reproductive parameters of male diabetic animals.

Methods

A total of 48 Wistar rats were distributed into six groups: diabetes (n = 8); diabetes and Brazil nut extract (n = 8); diabetes and sodium selenite (Na₂SeO₃) (n = 8); Brazil nut extract (n = 8); sodium selenite (n = 8) and control (n = 8). A single dose of streptozotocin (65 mg/kg) was injected intravenously to the rats to induce diabetes. BN or Na₂SeO₃ were administered by gavage for 56 days.

Results

The diabetes caused critical alterations on body mass gain, reproductive parameters and antioxidant capacity. Treatments with both BN or Na₂SeO₃ were able to increase significantly the glutathione peroxidase and the daily sperm production, both in diabetic (p < 0.01 and p < 0.05) and in healthy animals (p < 0.01 and p < 0.05).

Conclusion

The Brazil nut extract and sodium selenite were able to improve some reproductive parameters of diabetic rats. Moreover, we could infer that this effect is probably due to the natural selenium content of the BN.

Depression-like behavior, hyperglycemia, oxidative stress, and neuroinflammation presented in diabetic mice are reversed by the administration of 1-methyl-3-(phenylselanyl)-1H-indole

Oxidative stress and neuroinflammation are found both in diabetes mellitus and major depressive disorder (MDD). In addition to damage in peripheral organs, such as liver and kidney, diabetic patients have a higher risk of developing depression. In this sense, the objective of the present study was to characterize the antidepressant-like effect of a selenium-containing compound, the 1-methyl-3-(phenylselanyl)-1H-indole (MFSeI), in streptozotocin (STZ)-induced diabetic mice. STZ (200 mg/kg, i.p.) was used to induce diabetes mellitus type I, and after seven days, the administration of MFSeI (10 mg/kg, i.g.) was initiated and followed for the next 14 days. Twenty-four hours after the last administration of MFSeI, the behavioral tests were performed, followed by euthanasia. The treatment with MFSeI was able to reverse the hyperglycemia induced by STZ. MFSeI also decreased the plasma levels of biomarkers of liver and kidney damage. Importantly, MFSeI reversed the depression-like behavior induced by STZ in the tail suspension test and forced swimming test without promoting locomotor alterations. Furthermore, MFSeI reversed the increased levels of reactive species and lipid peroxidation in the prefrontal cortex (PFC), hippocampus (HC), liver, and kidney of STZ-treated mice. Treatment with MFSeI also decreased the expression of tumor necrosis factor-alpha, inducible nitric oxide synthase and indoleamine 2,3-dioxygenase, while increasing the expression of interleukin-10, insulin receptor substrate-1 and glucose transport-4 in the PFC and HC of mice. Taken together, the results indicate the effectiveness of MFSeI against depression-like behavior and central and peripheral complications caused by diabetes in mice.

Association between Serum Selenium Level and the Presence of Diabetes Mellitus: A Meta-Analysis of Observational Studies

BACKGROUND

Epidemiological studies have suggested an association between selenium (Se) and diabetes mellitus (DM). However, different studies have reported conflicting results. Therefore, we performed a comprehensive meta-analysis to clarify the impact of Se on DM.

METHODS

We searched the PubMed database for studies on the association between Se and DM from inception to June 2018.

RESULTS

Twenty articles evaluating 47,930 participants were included in the analysis. The meta-analysis found that high levels of Se were significantly associated with the presence of DM (pooled odds ratios [ORs], 1.88; 95% confidence interval [CI], 1.44 to 2.45). However, significant heterogeneity was found (I²=82%). Subgroup analyses were performed based on the Se measurement methods used in each study. A significant association was found between high Se levels and the presence of DM in the studies that used blood (OR, 2.17; 95% CI, 1.60 to 2.93; I²=77%), diet (OR, 1.61; 95% CI, 1.10 to 2.36; I²=0%), and urine (OR, 1.49; 95% CI, 1.02 to 2.17; I²=0%) as samples to estimate Se levels, but not in studies on nails (OR, 1.24; 95% CI, 0.52 to 2.98; I²=91%). Because of significant heterogeneity in the studies with blood, we conducted a sensitivity analysis and tested the publication bias. The results were consistent after adjustment based on the sensitivity analysis as well as the trim and fill analysis for publication bias.

CONCLUSION

This meta-analysis demonstrates that high levels of Se are associated with the presence of DM. Further prospective and randomized controlled trials are warranted to elucidate the link better.

Vanadium in Biosphere and Its Role in Biological Processes

Ultra-trace elements or occasionally beneficial elements (OBE) are the new categories of minerals including vanadium (V). The importance of V is attributed due to its multifaceted biological roles, i.e., glucose and lipid metabolism as an insulin-mimetic, antilipemic and a potent stress alleviating agent in diabetes when vanadium is administered at lower doses. It competes with iron for transferrin (binding site for transportation) and with lactoferrin as it is secreted in milk also. The intracellular enzyme protein tyrosine phosphatase, causing the dephosphorylation at beta subunit of the insulin receptor, is inhibited by vanadium, thus facilitating the uptake of glucose inside the cell but only in the presence of insulin. Vanadium could be useful as a potential immune-stimulating agent and also as an antiinflammatory therapeutic metallodrug targeting various diseases. Physiological state and dose of vanadium compounds hold importance in causing toxicity also. Research has been carried out mostly on laboratory animals but evidence for vanadium importance as a therapeutic agent are available in humans and large animals also. This review examines the potential biochemical and molecular role, possible kinetics and distribution, essentiality, immunity, and toxicity-related study of vanadium in a biological system.

Pre-Clinical Study for the Antidiabetic Potential of Selenium Nanoparticles

This research was delineated to explore the efficacy of selenium nanoparticles delivered in liposomes (L-Se) in the mitigation of type-2 diabetes mellitus. Adult female Wistar rats were assigned into four groups: group I, the normal control group in which the rats received normal saline solution orally; group II, the diabetic control group in which the rats were injected intraperitoneally with a single dose of streptozotocin (STZ) for induction of diabetes; group III, the metformin (Met)-treated group in which the diabetic rats were treated orally with Met; and group IV, the L-Se-treated group in which the diabetic rats were treated orally with L-Se. All treatments were delivered for 21 days. Blood and pancreas tissue samples were obtained for biochemical analysis, immunohistochemical examinations, and histopathological investigation. The L-Se-treated group showed significant drop in serum glucose and pancreatic malondialdehyde (MDA), nitric oxide (NO), tumor necrosis factor-α (TNF-α), and prostaglandin F2α (PGF2α) levels associated with significant rise in serum insulin and pancreatic glutathione, superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx), and glutathione reductase (GR) values, in addition to significant improvement in the immunohistochemical indices (insulin and glucagon). Aforementioned results are appreciated by the histopathological findings of pancreatic tissue. In conclusion, our data have brought about compelling evidence favoring the antidiabetic potency of elemental selenium nanoparticles delivered in liposomes through preservation of pancreatic β cell integrity with consequent increment of insulin secretion and in turn glucose depletion, repression of oxidative stress, potentiation of the antioxidant defense system, and inhibition of pancreatic inflammation.

High dietary selenium intake is associated with less insulin resistance in the Newfoundland population

As an essential nutrient, Selenium (Se) is involved in many metabolic activities including mimicking insulin function. Data on Se in various biological samples and insulin resistance are contradictory, moreover there is no large study available regarding the relationship of dietary Se intake with insulin resistance in the general population. To investigate the association between dietary Se intake and variation of insulin resistance in a large population based study, a total of 2420 subjects without diabetes from the CODING (Complex Diseases in the Newfoundland Population: Environment and Genetics) study were assessed. Dietary Se intake was evaluated from the Willett Food Frequency questionnaire. Fasting blood samples were used for the measurement of glucose and insulin. Insulin resistance was determined with the homeostasis model assessment (HOMA-IR). Body composition was measured using dual energy X-ray absorptiometry. Analysis of covariance showed that high HOMA-IR groups in both males and females had the lowest dietary Se intake (μg/kg/day) (p < 0.01), being 18% and 11% lower than low HOMA-IR groups respectively. Insulin resistance decreased with the increase of dietary Se intake in females but not in males after controlling for age, total calorie intake, physical activity level, serum calcium, serum magnesium, and body fat percentage (p < 0.01). Partial correlation analysis showed that dietary Se intake was negatively correlated with HOMA-IR after adjusting for the Se confounding factors in subjects whose dietary Se intake was below 1.6 μg/kg/day (r = -0.121 for males and -0.153 for females, p < 0.05). However, the negative correlation was no longer significant when dietary Se intake was above 1.6 μg/kg/day. Our findings suggest that higher dietary Se intake is beneficially correlated with lower insulin resistance when total dietary Se intake was below 1.6 μg/kg/day. Above this cutoff, this beneficial effect disappears.

Selenoprotein SelK increases the secretion of insulin from MIN6 β cells

The expression of selenoprotein SelK triggers the secretion of insulin from MIN6 β cells by increasing the cytosolic free Ca²⁺ level, resulting from the up-regulated IP3R3 expression.

Anti-hyperglycemic activity of selenium nanoparticles in streptozotocin-induced diabetic rats

The study was designed to investigate the anti-hyperglycemic activity of selenium nanoparticles (SeNPs) in streptozotocin-induced diabetic rats. Fifty-five mg/kg of streptozotocin was injected in rats to induce diabetes. Animals either treated with SeNPs alone or with insulin (6 U/kg) showed significantly decreased fasting blood glucose levels after 28 days of treatment. The serum insulin concentration in untreated diabetic animals was also enhanced by SeNPs. The results demonstrated that SeNPs could significantly decrease hepatic and renal function markers, total lipid, total cholesterol, triglyceride and low-density lipoprotein cholesterol levels, and glucose-6-phosphatase activity. At the same time, SeNPs increased malic enzyme, hexokinase and glucose-6-phosphate dehydrogenase activity, liver and kidney glycogen contents, and high-density lipoprotein cholesterol levels. In addition, SeNPs were able to prevent the histological injury in the hepatic and renal tissues of rats. However, insulin injection also exhibited a significant improvement in diabetic animals after 28 days of treatment. This study suggests that SeNPs can alleviate hyperglycemia and hyperlipidemia in streptozotocin-induced diabetic rats, possibly by eliciting insulin-mimetic activity.

Effects of selenium on endothelial dysfunction and metabolic profile in low dose streptozotocin induced diabetic rats fed a high fat diet

Endothelial dysfunction develops as a result of oxidative stress and is responsible for diabetic vascular complications. We investigated the effects of selenium on endothelial dysfunction and oxidative stress in type 2 diabetic rats. Male Wistar rats were divided into five groups: controls, untreated diabetics, and diabetics treated with 180, 300, 500 mcg/kg selenium each day. Diabetes was induced by a single intraperitoneal injection of low dose streptozotocin to rats fed a high fat diet. Endothelium-dependent and -independent relaxations were measured in the thoracic aorta. Nicotinamide adenine dinucleotide phosphate (NADPH) oxidase and endothelial nitric oxide synthase (eNOS) mRNA expressions were analyzed using real-time polymerase chain reaction (RT-PCR). Fasting blood glucose, lipid profile, lipid oxidation, insulin and nitric oxide were measured in blood samples. Malondialdehyde, superoxide dismutase, catalase and glutathione peroxidase levels were measured in liver samples. RT-PCR showed that selenium reversed increased NADPH oxidase expression and decreased eNOS expression to control levels. Selenium also improved the impairment of endothelium-dependent vasorelaxation in the diabetic aorta. Selenium treatment significantly decreased blood glucose, cholesterol and triglyceride levels, and enhanced the antioxidant status in diabetic rats. Our findings suggest that selenium restores a normal metabolic profile and ameliorates vascular responses and endothelial dysfunction in diabetes by regulating antioxidant enzyme and nitric oxide release.

Selenium and diabetes--evidence from animal studies

Whereas selenium was found to act as an insulin mimic and to be antidiabetic in earlier studies, recent animal experiments and human trials have shown an unexpected risk of prolonged high Se intake in potentiating insulin resistance and type 2 diabetes. Elevating dietary Se intake (0.4 to 3.0mg/kg of diet) above the nutrient requirements, similar to overproduction of selenoproteins, led to insulin resistance and/or diabetes-like phenotypes in mice, rats, and pigs. Although its diabetogenic mechanism remains unclear, high Se intake elevated activity or production of selenoproteins including GPx1, MsrB1, SelS, and SelP. This upregulation diminished intracellular reactive oxygen species and then dysregulated key regulators of β cells and insulin synthesis and secretion, leading to chronic hyperinsulinemia. Overscavenging intracellular H2O2 also attenuated oxidative inhibition of protein tyrosine phosphatases and suppressed insulin signaling. High Se intake might affect expression and/or function of key regulators of glycolysis, gluconeogenesis, and lipogenesis. Future research is needed to find out if certain forms of Se metabolites in addition to selenoproteins and if mechanisms other than intracellular redox control mediate the diabetogenic effects of high Se intake. Furthermore, a potential interactive role of high Se intake in the interphase of carcinogenesis and diabetogenesis should be explored to make optimal use of Se in human nutrition and health.

Selenium significantly inhibits adipocyte hypertrophy and abdominal fat accumulation in OLETF rats via induction of fatty acid β-oxidation

A combination of selenium (Se) with other trace element is associated with partially modulate fatty acid distribution as well as reduction of the body weight and feed efficiency. To investigate whether or not Se treatment has an impact on lipid metabolism, we examined the levels of lipid metabolism-related factors, including abdominal fat, adiponectin, cholesterol, very long chain dehydrogenase (VLCAD), and medium chain acyl-CoA dehydrogenase (MCAD) in 20-week-old Otsuka Long-Evans Tokushima Fatty (OLETF) rats following sodium selenite treatment for 2 weeks. Herein, we observed that (a) Se treatment induced insulin-like effects by lowering the serum glucose level in rats; (b) Se-treated rats showed significance values decreases in abdominal fat mass, adipocyte size, and adiponectin, which are associated with lipid metabolism; (c) Se treatment led to reduced levels of cholesterol, triglycerides, low-density lipoprotein (LDL), and high-density lipoprotein (HDL) cholesterol; (d) fat tissue in Se-treated rats displayed significantly lower expression of adipocyte marker genes along with increased expression of VLCAD and MCAD; and (e) fatty liver formation and β-oxidation gene expression were both significantly reduced in liver tissue of Se-treated rats. Therefore, our results suggest that Se may induce inhibition of adipocyte hypertrophy and abdominal fat accumulation along with suppression of fatty liver formation by the differential regulation of the gene expression for fatty acid β-oxidation in the OLETF model.

Effect of selenium on connexin expression, angiogenesis, and antioxidant status in diabetic wound healing

This study was done to analyze the effect of selenium on antioxidant status and expression of different connexins in diabetic wound healing. The levels of vascular endothelial growth factor, superoxide dismutase, lipid peroxide, and connexins were analyzed in wound tissues taken from diabetic and non-diabetic mice before and after sodium selenite administration. The mRNA transcript levels of Cx 26, 30.3, 31, 31.1, and 43 were significantly elevated in diabetic wounds as compared to the non-diabetic wounds. After selenium administration, the expression of connexins along with serum glucose decreases more significantly in diabetic wounds as compared to non-diabetic wounds. In diabetic wounds, the low levels of vascular endothelial growth factor and extracellular superoxide dismutase were restored to normal level following selenium administration. The lipid peroxidation decreased significantly in diabetic mice post-selenium administration. The histopathological analysis revealed that administration of selenium improves angiogenesis at the wound site. The results of this study demonstrate that selenium, acting as an essential component of the antioxidant system, normalizes the antioxidant status, and as an insulin mimetic compound, downregulates connexin expressions and induces angiogenesis. Together, these effects of selenium accelerate wound healing in diabetic conditions.

Delaying of insulin signal transduction in skeletal muscle cells by selenium compounds

Supranutritional selenium (Se) intake and high serum Se levels have been associated epidemiologically with increased risk for type 2 diabetes, suggesting adverse effects of dietary Se compounds and/or antioxidant selenoenzymes on the sensitivity of target tissues for insulin. Here, we compared the capability of inorganic (sodium selenite and sodium selenate) and organic (selenomethionine and methylseleninic acid (MSeA)) Se compounds to interfere with insulin signaling in rat L6 myotubes, differentiated skeletal muscle cells. When applied at doses of 1 μM, only selenite and MSeA were capable of delaying insulin-induced phosphorylation of protein kinase B (Akt) and attenuating insulin-induced phosphorylation of forkhead box class O transcription factors FoxO1a and FoxO3. Insulin-stimulated glucose uptake was lowered by selenite and MSeA as well. Even though all tested Se compounds strongly stimulated expression/activity of the cellular selenoproteins glutathione peroxidase 1 and selenoprotein W, selenite and MSeA were the most efficiently utilized Se donors. Moreover, at doses of 1 μM, only selenite and MSeA had a significant inhibitory effect on generation of intracellular reactive oxygen species (ROS). These results suggest that the Se(IV) compounds selenite and MSeA may impair the insulin sensitivity of myocytes by influencing cellular redox homeostasis.

High selenium intake and increased diabetes risk: experimental evidence for interplay between selenium and carbohydrate metabolism

The essential trace element selenium has long been considered to exhibit anti-diabetic and insulin-mimetic properties, but recent epidemiological studies indicated supranutritional selenium intake and high plasma selenium levels as possible risk factors for development of type 2 diabetes, pointing to adverse effects of selenium on carbohydrate metabolism in humans. However, increased plasma selenium levels might be both a consequence and a cause of diabetes. We summarize current evidence for an interference of selenium compounds with insulin-regulated molecular pathways, most notably the phosphoinositide-3-kinase/protein kinase B signaling cascade, which may underlie some of the pro- and anti-diabetic actions of selenium. Furthermore, we discuss reports of hyperinsulinemia, hyperglycemia and insulin resistance in mice overexpressing the selenoenzyme glutathione peroxidase 1. The peroxisomal proliferator-activated receptor gamma coactivator 1α represents a key regulator for biosynthesis of the physiological selenium transporter, selenoprotein P, as well as for hepatic gluconeogenesis. As proliferator-activated receptor gamma coactivator 1α has been shown to be up-regulated in livers of diabetic animals and to promote insulin resistance, we hypothesize that dysregulated pathways in carbohydrate metabolism and a disturbance of selenium homeostasis are linked via proliferator-activated receptor gamma coactivator 1α.

Selenomethionine stimulates expression of glutathione peroxidase 1 and 3 and growth of bovine mammary epithelial cells in primary culture

This study examined the localization of cellular glutathione peroxidase (GPx1) and extracellular glutathione peroxidase (GPx3) in lactating mammary tissue and in primary cultures of bovine mammary epithelial cells (BMEC). The effect of selenium as selenomethionine (SeMet) on the growth and viability of BMEC and GPx protein expression and activity were also studied. Single mammary epithelial cells were recovered by serial collagenase/hyaluronidase digestion from lactating bovine mammary tissue and cultured in a low-serum collagen gel system enriched with lactogenic hormones and 0, 10, 20, or 50 nM SeMet. Positive immunostaining with anti-cytokeratin and bovine anti-casein confirmed the epithelial nature and differentiated state of BMEC. Addition of SeMet to media facilitated rapid confluence of BMEC and formation of dome structures. Immunohistochemical and immunocytochemical staining revealed that both GPx1 and GPx3 are synthesized by BMEC and localized in the cytoplasm and nucleus. Up to 50 nM SeMet linearly increased BMEC number and viability over 5 d of culture. Bovine mammary epithelial cells cultured in SeMet-supplemented medium also exhibited markedly elevated GPx activity and linear increases in abundance of GPx1 and GPx3 proteins. It is apparent that SeMet degradation to release Se for synthesis of selenoproteins is carried out by BMEC. Results indicate that bovine mammary epithelial cells express GPx1 and GPx3 in vivo and in vitro; SeMet enhances expression of these selenoproteins in vitro and the growth and viability of BMEC.

In vitro growth inhibition of mouse mammary epithelial tumor cells by methylseleninic acid: involvement of protein kinases

Methylseleninic acid (MSeA) is a synthetic organoselenium form known to be effective against mammary carcinogenesis in vivo. Using the synchronized mouse mammary epithelial tumor cell (TM6) model, we have previously shown that 5 microM MSeA significantly inhibits cell growth and induces a reversible growth arrest in the G1 phase. In the present study, we examined the effects of MSeA on Rb, cyclin dependent kinase 2 (cdk2), cdk4, cyclin E and cyclin D1. Growth arrest of cells was accompanied by a reduction in total cdk2 kinase and cyclin E-associated cdk2 kinase activities. The p27 levels associated with cdk2 were elevated during the cell cycle. In addition, growth inhibition correlated with a relative increase in the hypophosphorylated form of Rb in MSeA-treated cells and Egr1 was elevated in MSeA-treated cells. The Kinetworks Protein Kinase Screen (KPKS 1.0) was used to examine 75 protein kinases. MSeA treatment resulted in differential expression of several protein-serine/threonine kinases, protein-tyrosine kinases and protein-threonine/tyrosine kinases. Some of these kinases are being reported for the first time as being altered by MSeA. The outcome of these experiments will be of significance since these kinases are known to be involved in survival and/or apoptotic pathways of tumor cells.

Effect of vanadate on gene expression of the insulin signaling pathway in skeletal muscle of streptozotocin-induced diabetic rats

An insulin signaling pathway microarray was used to evaluate the gene expression profiling of the insulin signaling pathway in the skeletal muscle of streptozotocin-induced diabetic, NaVO(3)-treated diabetic and insulin-treated diabetic rats for the investigation of the effect of vanadium and insulin on the insulin signaling pathway. Of 96 genes surveyed, transcriptional patterns of 19 genes (20%) showed alterations in diabetic rats compared with controls. Although most of these changed gene expressions were improved after treatment with NaVO(3) (14, 74%) and insulin (16, 84%), NaVO(3) and insulin treatment resulted in the alteration of 20 and 12 additional gene transcripts compared no treatment. We found that both NaVO(3) and insulin treatment achieved a desirable glucose level and most of the alterative gene transcripts in diabetic rats were normalized with NaVO(3) and insulin treatment. Comparison of the gene expression profiling indicates that there is a significant difference between the NaVO(3)-treated group and the insulin-treated group. The present study demonstrated for the first time that several candidate genes of the insulin signaling pathway are involved in the effect of vanadium treatment on hyperglycemia. This study opens the way for more focused investigations that may identify the genes responsible for diabetes and vanadium treatment in the global insulin signaling pathway.

Selenium acts as an insulin-like molecule for the down-regulation of diabetic symptoms via endoplasmic reticulum stress and insulin signalling proteins in diabetes-induced non-obese diabetic mice

To investigate whether selenium (Sel) treatment would impact on the onset of diabetes,we examined serum biochemical components including glucose and insulin,endoplasmic reticulum (ER) stress and insulin signalling proteins, hepatic C/EBP-homologous protein (CHOP) expression and DNA fragmentation in diabetic and non- diabetic conditions of non-obese diabetic (NOD) mice. We conclude that (i) Sel treatment induced insulin-like effects in lowering serum glucose level in Sel-treated NOD mice, (ii) Sel-treated mice had significantly decreased serum biochemical components associated with liver damage and lipid metabolism, (iii) Sel treatment led to the activation of the ER stress signal through the phosphorylation of JNK and eIF2 protein and insulin signal mechanisms through the phosphorylation of Akt and PI3 kinase, and (iv) Sel-treated mice were significantly relieved apoptosis of liver tissues indicated by DNA fragmentation assay in the diabetic NOD group. These results suggest that Sel compounds not only serve as insulin-like molecules for the downregulation of glucose level and the incidence of liver damage, but may also have the potential for the development of new drugs for the relief of diabetes by activating the ER stress and insulin signalling pathways.

Polymorphism of selected enzymes involved in detoxification and biotransformation in relation to lung cancer

Available data indicate that there are significant differences in individual susceptibility to lung cancer within the human population. It is believed to be underlie by inherited genetic predispositions related to the genetic polymorphism of several enzymes involved in the detoxification and xenobiotic metabolism. In this review, we collect and discuss the evidence reported up to date on the association between lung cancer and genetic polymorphism of cytochromes P450, N-acetyltransferase, glutathione S-transferases, microsomal epoxide hydrolase, NAD(P)H:quinone oxidoreductase, myeloperoxidase and glutathione peroxidase. All these genes might appear to be candidates for lung cancer susceptibility genes, nevertheless, the present state of the art still offers only a limited explanation of the link between such polymorphisms and increased risk of lung cancer.

Differential effects of selenium compounds on glucose synthesis in rabbit kidney-cortex tubules and hepatocytes. In vitro and in vivo studies

Although selenium is taken with diet mainly as selenoamino acids, its hypoglycaemic action on hepatic gluconeogenesis has been studied with the use of inorganic selenium derivatives. The aim of the present investigation was to compare relative efficacies of inorganic and organic selenium compounds in reducing glucose synthesis in hepatocytes and renal tubules, significantly contributing to the glucose homeostasis. In contrast to hepatocytes, both selenite and methylselenocysteine inhibited renal gluconeogenesis by about 40-45% in control rabbits. Selenate did not affect this process, whereas selenomethionine inhibited gluconeogenesis by about 20% in both hepatocytes and renal tubules. In contrast to methylselenocysteine, selenite decreased intracellular ATP content, glutathione reduced/glutathione oxidized (GSH/GSSG) ratio and pyruvate carboxylase, PEPCK and FBPase activities, while methylselenocysteine diminished PEPCK activity due to elevation of intracellular 2-oxoglutarate and GSSG, inhibitors of this enzyme. Experiments in vivo indicate that in 3 of 9 alloxan-diabetic rabbits treated for 14 days with methylselenocysteine (0.182mg/kg body weight) blood glucose level was normalized, whereas in all diabetic rabbits plasma creatinine and urea levels decreased from 2.52+/-0.18 and 87.4+/-9.7 down to 1.63+/-0.11 and 39.0+/-2.8, respectively. In view of these data selenium supplementation might be beneficial for protection against diabetes-induced nephrotoxicity despite selenium accumulation in kidneys and liver.

Selenium alters the lipid content and protein profile of rat heart: an FTIR microspectroscopic study

Cardiovascular disease is one of the most important causes of morbidity and mortality in Western countries. In addition, it is well documented that selenium (Se) deficiency has been linked to cardiovascular diseases. This study was undertaken to present the effect of sodium selenite on left and right myocardia, and small veins of normal control rat heart at molecular level by using Fourier transform infrared (FTIR) microspectroscopy. The results mainly reveal that, Se treatment causes an increase in lipid content both in the saturated and unsaturated lipids, and an alteration in protein profile with a decrease in alpha-helix and an increase in beta-sheet structure of the rat heart which might be reflecting a slight subtoxic effect of selenium supplementation on normal rat heart at the dose used in this study.

Selenium prevents diabetes-induced alterations in [Zn2+]iand metallothionein level of rat heart via restoration of cell redox cycle

Intracellular free zinc concentration ([Zn2+]i) is very important for cell functions, and its excessive accumulation is cytotoxic. [Zn2+]ican increase rapidly in cardiomyocytes because of mobilization of Zn2+from intracellular stores by reactive oxygen species (ROS). Moreover, ROS have been proposed to contribute to direct and/or indirect damage to cardiomyocytes in diabetes. To address these hypotheses, we investigated how elevated [Zn2+]iin cardiomyocytes could contribute to diabetes-induced alterations in intracellular free calcium concentration ([Ca2+]i). We also investigated its relationship to the changes of metallothionein (MT) level of the heart. Cardiomyocytes from normal rats loaded with fura-2 were used to fluorometrically measure resting [Zn2+]i(0.52 ± 0.06 nM) and [Ca2+]i(26.53 ± 3.67 nM). Fluorescence quenching by the heavy metal chelator N, N, N′, N′-tetrakis(2-pyridylmethyl)ethylenediamine was used to quantify [Zn2+]i. Our data showed that diabetic cardiomyocytes exhibited significantly increased [Zn2+]i(0.87 ± 0.05 nM ) and [Ca2+]i(49.66 ± 9.03 nM), decreased levels of MT and reduced glutathione, increased levels of lipid peroxidation and nitric oxide products, and decreased activities of superoxide dismutase, glutathione reductase, and glutathione peroxidase. Treatment (4 wk) of diabetic rats with sodium selenite (5 μmol·kg body wt−1·day−1) prevented these defects induced by diabetes. A comparison of present data with previously observed beneficial effects of selenium treatment on diabetes-induced contractile dysfunction of the heart can suggest that an increase in [Zn2+]imay contribute to oxidant-induced alterations of excitation-contraction coupling in diabetes. In addition, we showed that oxidative stress is involved in the etiology of diabetes-induced downregulation of heart function via depressed endogenous antioxidant defense mechanisms.

Compendium of the antidiabetic effects of supranutritional selenate doses. In vivo and in vitro investigations with type II diabetic db/db mice

In recent years, a number of investigations on the antidiabetic effects of supranutritional selenate doses have been carried out. Selenate (selenium oxidation state +VI) was shown to possess regulatory effects on glycolysis, gluconeogenesis and fatty acid metabolism, metabolic pathways which are disturbed in diabetic disorders. An enhanced phosphorylation of single components of the insulin signalling pathway could be shown to be one molecular mechanism responsible for the insulinomimetic properties of selenate. In type II diabetic animals, a reduction of insulin resistance could be shown as an outcome of selenate treatment. The present study with db/db mice was performed to investigate the antidiabetic mechanisms of selenate in type II diabetic animals. Twenty-one young adult female db/db mice were randomly assigned to three experimental groups (selenium deficient=0Se, selenite-treated group=SeIV and selenate-treated group=SeVI) with seven animals each. Mice of all groups were fed a selenium-deficient diet for 8 weeks. The animals of the groups SeIV and SeVI were supplemented with increasing amounts of sodium selenite or sodium selenate up to 35% of the LD50 in week 8 in addition to the diet by tube feeding. Selenate treatment reduced insulin resistance significantly and reduced the activity of liver cytosolic protein tyrosine phosphatases (PTPs) as negative regulators of insulin signalling by about 50%. In an in vitro inhibition test selenate (oxidation state +VI) per se did not inhibit PTP activity. In this test, however, selenium compounds of the oxidation state +IV were found to be the actual inhibitors of PTP activity. Selenate administration in vivo further led to characteristic changes in the selenium-dependent redox system, which could be mimicked in an in vitro assay and provided further evidence for the intermediary formation of SeIV metabolites. The expression of peroxisome proliferator-activated receptor gamma (PPARgamma), another important factor in the context of insulin resistance and lipid metabolism, was significantly increased by selenate application. In particular, liver gluconeogenesis and lipid metabolism were influenced strongly by selenate treatment. In conclusion, our results showed that supranutritional selenate doses influenced two important mechanisms involved in insulin-resistant diabetes, namely, PTPs and PPARgamma, which, in turn, can be assumed as being responsible for the changes in intermediary metabolism, e.g., gluconeogenesis and lipid metabolism. The initiation of these mechanisms thereby seems to be coupled to the intermediary formation of the selenium oxidation state +IV (selenite state) from selenate.

Selenomethionine stimulates MAPK (ERK) phosphorylation, protein oxidation, and DNA synthesis in gastric cancer cells

Selenium is an essential trace element and is required for the synthesis of cellular enzymes that protect against oxidative stress. Epidemiological findings indicate that low selenium intake is associated with increased cancer risk, and, although the majority of studies show that exposure of transformed cells to selenium results in apoptotic cell death, there are reports indicating that cells exposure to low selenium concentrations promotes cellular proliferation. Gastric adenocarcinoma SNU-1 cells responded to selenomethionine with a biphasic proliferative curve: enhanced incorporation of 3H-thymidine into DNA within a very narrow range of selenomethionine concentrations followed by decreased 3H-thymidine uptake at higher levels. Concentrations of selenomethionine that stimulate cellular proliferation also induce cellular oxidation and phosphorylation of MAPK (ERK), a component of cell signaling cascades. MAPK (ERK) phosphorylation is synonymous with MAPK activation and enhanced cell growth. Our findings support previous observations of enhanced proliferation in response to low levels of selenium and suggest that, at certain concentrations, selenomethionine induces mild oxidative stress that, in turn, stimulates DNA synthesis.

Effects of a supranutritional dose of selenate compared with selenite on insulin sensitivity in type II diabetic dbdb mice

The present study was performed to examine the mechanism by which selenate ameliorates the insulin sensitivity in type II diabetic dbdb mice. Therefore, 21-adult female dbdb mice were randomly assigned to three experimental groups (0Se, SeIV and SeVI) with seven animals per group. Mice of group 0Se were fed with a selenium-deficient diet (<0.02 mg Se/kg) based on wheat and torula yeast for 8 weeks whereas the mice of groups SeIV (selenite) and SeVI (selenate) were fed with sodium selenite and sodium selenate (up to 35% of the LD(50) for mice in eighth week), in addition to the diet by daily tube feeding. Eight weeks of selenate application led to significantly elevated insulin sensitivity in comparison with selenium deficiency and selenite application. The activity of cytosolic protein tyrosine phosphatases (PTPs) as important negative regulators of insulin signalling was reduced from 53.8% to 22.5% in the liver and skeletal muscle of selenate-treated mice in comparison with the selenium deficient and selenite-treated controls, suggesting an inhibition of PTPs by intermediary selenate metabolites. In an additional in vitro inhibition study, selenate (oxidation state +VI) did not inhibit PTP activity. Selenium metabolites in the oxidation state +IV were found to be the actual inhibitors of PTP activity. In conclusion, the results of the present study show that one possible mechanism by which supranutritional selenate doses enhance insulin sensitivity in type II diabetic dbdb mice is based on the inhibition of PTPS as negative regulators of insulin signalling. Moreover the cellular metabolism of selenate including its intermediary reduction to the oxidation state +IV seems to play a crucial role during this process.

Selenium-induced alterations in ionic currents of rat cardiomyocytes

In the present study, rats were treated with sodium selenite (5 micromol/kg body weight/day, ip) for 4 weeks and the parameters of contractile activity, action potential, L-type Ca2+-current (ICaL), as well as transient outward (Ito), inward rectifier (IK1), and steady state (Iss) K+-currents were investigated. Sodium selenite treatment increased rat blood glucose level and lowered plasma insulin level, significantly. This treatment also caused slightly prolongation in action potential with no significant effects on spontaneous contraction parameters and intracellular Ca2+ transients of the heart preparations. These effects were associated with marked alterations in the kinetics of both ICaL and Ito including a significant slowing in both inactivation time constants of ICaL and a significant shift to negative potential at half-inactivation of these channels without any change in the current density. Also, there was a significantly faster inactivation of Ito and no shift in half-inactivation of this channel without any change in its current density. Consequently, there was a approximately 50% increase in total charges carried by Ca2+ current and approximately 50% decrease in total charges carried by K+ currents of the treated rat cardiomyocytes. Additionally we observed a significant inhibition in IK1 density in treated rat cardiomyocytes. Oxidized glutathione level was significantly increased (70%) while the observed decrease in reduced glutathione was much less. Since a shift in redox state of regulatory proteins is related with cell dysfunction, selenium-induced increase in blood glucose and decrease in plasma insulin may correlate these alterations. These alterations, in the kinetics of the channels and in IK1 density, might lead to proarrhythmic effect of chronic selenium supplementation.

Selenium and brain function: a poorly recognized liaison

Molecular biology has recently contributed significantly to the recognition of selenium (Se)2 and Se-dependent enzymes as modulators of brain function. Increased oxidative stress has been proposed as a pathomechanism in neurodegenerative diseases including, among others, Parkinson's disease, stroke, and epilepsy. Glutathione peroxidases (GPx), thioredoxin reductases, and one methionine-sulfoxide-reductase are selenium-dependent enzymes involved in antioxidant defense and intracellular redox regulation and modulation. Selenium depletion in animals is associated with decreased activities of Se-dependent enzymes and leads to enhanced cell loss in models of neurodegenerative disease. Genetic inactivation of cellular GPx increases the sensitivity towards neurotoxins and brain ischemia. Conversely, increased GPx activity as a result of increased Se supply or overexpression ameliorates the outcome in the same models of disease. Genetic inactivation of selenoprotein P leads to a marked reduction of brain Se content, which has not been achieved by dietary Se depletion, and to a movement disorder and spontaneous seizures. Here we review the role of Se for the brain under physiological as well as pathophysiological conditions and highlight recent findings which open new vistas on an old essential trace element.

GPx-1 modulates Akt and P70S6K phosphorylation and Gadd45 levels in MCF-7 cells

Selenium has been shown to prevent cancer in animal models, and recent data indicate it is likely to be effective in humans as well. One selenium-containing protein, the cytoplasmic form of glutathione peroxidase (GPx-1), has been implicated in cancer risk and development by genetic studies identifying at-risk alleles and loss of heterozygosity in tumors. In order to evaluate the biological consequences of GPx-1 overexpression, human MCF-7 cells were stably transfected with a GPx-1 expression construct and the effects of GPx-1 on protein kinases associated with stress responses were determined. GPx-1 overexpression affected phosphorylation of p70S6K, whereas Erk1/2 and p38 MAPK were not affected. Site-specific phosphorylation of Akt declined and the levels of Gadd45, a DNA damage response protein, increased significantly as a consequence of elevated GPx-1 expression. Effects on p70S6K and Gadd45 after selenium supplementation have been reported, and given previous data demonstrating a role for GPx-1 in cancer etiology, these results support the concept that the chemopreventive properties of selenium may be due, at least in part, to its role in regulating GPx-1.

Effects of selenium on altered mechanical and electrical cardiac activities of diabetic rat

Since selenium compounds can restore some metabolic parameters and structural alterations of diabetic rat heart, we were tempted to investigate whether these beneficial effects extend to the diabetic rat cardiac dysfunctions. Diabetes was induced by streptozotocin (50mg/kg body weight) and rats were then treated with sodium selenite (5 micromol/kg body weight/day) for four weeks. Electrically stimulated isometric contraction and intracellular action potential in isolated papillary muscle strips and transient (I(to)) and steady state (I(ss)) outward K(+) currents in isolated cardiomyocytes were recorded. Sodium selenite treatment could reverse the prolongation in both action potential duration and twitch duration of the diabetic rats, and also cause significant increases in the diminished amplitudes of the two K(+) currents. Treatment of rats with sodium selenite also markedly increased the depressed acid-soluble sulfhydryl levels of the hearts. Our data suggest that the beneficial effects of sodium selenite treatment on the mechanical and electrical activities of the diabetic rat heart appear to be due to the restoration of the diminished K(+) currents, partially, related to the restoration of the cell glutathione redox cycle.

Selenoprotein-deficient transgenic mice exhibit enhanced exercise-induced muscle growth

Dietary intake of selenium has been implicated in a wide range of health issues, including aging, heart disease and cancer. Selenium deficiency, which can reduce selenoprotein levels, has been associated with several striated muscle pathologies. To investigate the role of selenoproteins in skeletal muscle biology, we used a transgenic mouse (referred to as i6A-) that has reduced levels of selenoproteins due to the introduction and expression of a dominantly acting mutant form of selenocysteine transfer RNA (tRNA[Ser]Sec). As a consequence, each organ contains reduced levels of most selenoproteins, yet these mice are normal with regard to fertility, overall health, behavior and blood chemistries. In the present study, although skeletal muscles from i6A- mice were phenotypically indistinguishable from those of wild-type mice, plantaris muscles were approximately 50% heavier after synergist ablation, a model of exercise overload. Like muscle in wild-type mice, the enhanced growth in the i6A- mice was completely blocked by inhibition of the mammalian target of rapamycin (mTOR) pathway. Muscles of transgenic mice exhibited increased site-specific phosphorylation on both Akt and p70 ribosomal S6 kinase (p70S6k) (P < 0.05) before ablation, perhaps accounting for the enhanced response to synergist ablation. Thus, a single genetic alteration resulted in enhanced skeletal muscle adaptation after exercise, and this is likely through subtle changes in the resting phosphorylation state of growth-related kinases.

The chemical form of selenium affects insulinomimetic properties of the trace element: investigations in type II diabetic dbdb mice

The objective of the present study was to investigate the effects of oral selenate application in comparison to selenium deficiency and selenite treatment on the development of the diabetic status (glucose tolerance, insulin resistance and activities of glycolytic and gluconeogenic marker enzymes) in dbdb mice, representing a type II diabetic animal model. Therefore 21 adult male dbdb mice were assigned to 3 experimental groups of 7 animals each and put on a selenium deficient diet (< 0.03 mg/kg diet) based on torula yeast. Group 0Se was kept on selenium deficiency for 10 weeks while the mice of the groups SeIV and SeVI were supplemented daily with 15% of their individual LD(50) of sodium selenite or sodium selenate in addition to the diet. After 10 weeks a distinct melioration of the diabetic status indicated by a corrected glucose tolerance and a lowered insulin resistance was measured in selenate treated mice (group SeVI) in comparison to their selenium deficient and selenite treated companions and to their initial status. Activities of the glycolytic marker enzymes hexokinase, phosphofructokinase and pyruvate kinase were increased 1.7 to 3-fold in liver and/or adipose tissue by selenate treatment as compared to mice on selenium deficiency and mice with selenite administration. In contrast selenate treatment (SeVI) repressed the activity of liver pyruvate carboxylase the first enzyme in gluconeogenesis by about 33% in comparison to the selenium deficient (0Se) and selenite treated mice (SeIV). However the current study revealed an insulinomimetic role for selenate (selenium VI) also in type II diabetic animals due to a melioration of insulin resistance. In contrast selenium deficiency and especially selenite (selenium IV) impaired the diabetic status of dbdb mice, demonstrating the need for investigations on the insulinomimetic action of selenium due to the metabolism of different selenium compounds.

Selenite and selenomethionine promote HL-60 cell cycle progression

The essential role of selenium (Se) in nutrition is well established. The elucidation of the mechanisms by which selenium regulates the cell cycle can lead to a better understanding of the nature of selenium's essentiality and its role in disease prevention. In this study, the effects of selenium deficiency or adequacy (0.25 micromol/L selenite or selenomethionine) on HL-60 cell cycle progression were examined in serum-free media. Selenium was critical for promotion of HL-60 cell growth. Cell-cycle analysis revealed that selenium deficiency caused a decrease in G1 phase cells that corresponded to an increase in G2 and sub-G1 phase cells. Gene array analysis suggested that c-Myc, cyclin C, proliferating cell nuclear antigen, cyclin-dependent kinase (cdk)1, cdk2, cdk4, cyclin B and cyclin D2 mRNA levels were lower in selenium-deficient cells than in the cells supplemented with 0.25 micromol/L selenomethionine. The decrease in the c-Myc mRNA level in selenium-deficient cells was confirmed by reverse transcription-polymerase chain reaction analysis. Furthermore, the phosphorylation state of total cellular protein was higher (57%) in selenium-supplemented cells than in selenium-deficient cells. Collectively, these results suggest a novel role for selenium at 0.25 micromol/L in up-regulation of the expression of numerous cell cycle-related genes and total cellular phosphorylated proteins in HL-60 cells in serum-free culture media. This leads to the promotion of cell cycle progression, particularly G2/M transition and/or the reduction of apoptosis, primarily in G1 cells. These observations may have additional implications for understanding the nature of selenium's essentiality.

Selenium and the regulation of cell signaling, growth, and survival: molecular and mechanistic aspects

In the past 30 years, it has been recognized that dietary selenium (Se) is essential for the normal function of many of the systems of the body. Furthermore, low Se intake can have deleterious effects on several aspects of human and animal health. The importance of Se is characterized in its role as a constituent of several key antioxidant and redox enzyme families. Most of the effects of Se are probably mediated by selenoproteins, which have the micronutrient covalently incorporated into the protein. The purpose of this review is to examine basic mechanisms by which Se regulates cell growth, gene transcription, cell signaling, and cell death. We start with the historical background to Se. The synthesis and function of selenoproteins are described, followed by details of the dietary sources of Se and Se status in different parts of the world, together with the clinical effects of Se deficiency and toxicity. We consider some aspects of the molecular mechanisms by which Se modulates cell growth, intracellular signaling, and gene transcription.

Genistein affects lipogenesis and lipolysis in isolated rat adipocytes

Genistein is a phytoestrogen found in several plants eaten by humans and food-producing animals and exerting a wide spectrum of biological activity. In this experiment, the impact of genistein on lipogenesis and lipolysis was studied in isolated rat adipocytes. Incubation of the cells (10(6) cells/ml in plastic tubes at 37 degrees C with Krebs-Ringer buffer, 90 min) with genistein (0.01, 0.3, 0.6 and 1 mM) clearly restricted (1 nM) [U-14C]glucose conversion to total lipids in the absence and presence of insulin. When [14C]acetate was used as the substrate for lipogenesis, genistein (0.01, 0.1 and 1 mM) exerted a similar effect. Thus, the anti-lipogenetic action of genistein may be an effect not only of alteration in glucose transport and metabolism, but this phytoestrogen can also restrict the fatty acids synthesis and/or their esterification. Incubation of adipocytes with estradiol at the same concentrations also resulted in restriction of lipogenesis, but the effect was less marked. Genistein (0.1 and 1 mM) augmented basal lipolysis in adipocytes. This process was strongly restricted by insulin (1 microM) and H-89 (an inhibitor of protein kinase A; 50 microM) and seems to be primarily due to the inhibitory action of the phytoestrogen on cAMP phosphodiesterase in adipocytes. Genistein at the smallest concentration (0.01 mM) augmented epinephrine-stimulated (1 microM) lipolysis but failed to potentiate lipolysis induced by forskolin (1 microM) or dibutyryl-cAMP (1 mM). These results suggest genistein action on the lipolytic pathways before activation of adenylate cyclase. The restriction of lipolysis stimulated by several lipolytic agents--epinephrine, forskolin and dibutyryl-cAMP were observed when adipocytes were incubated with genistein at highest concentrations (0.1 and 1 mM). These results prove the inhibitory action of this phytoestrogen on the final steps of the lipolytic cascade, i.e. on protein kinase A or hormone sensitive lipase. Estradiol, added to the incubation medium, did not affect lipolysis. It can be concluded that genistein significantly affects lipogenesis and lipolysis in isolated rat adipocytes.